1. Technical Field
The present disclosure relates to methods for detecting electromagnetic waves and, particularly, to a carbon nanotube based method for detecting polarizing direction of electromagnetic waves.
2. Description of Related Art
Polarizing direction and intensity are two important properties of an electromagnetic wave. One method for detecting the polarizing direction of a visible light includes disposing a polarizer and a target in the path of the visible light, and rotating the polarizer. The polarized visible light goes through the polarizer and irradiates the target. As the polarizer rotates, the light on the target changes periodically from the dark to the bright. When the light on the target is darkest, the polarizing direction of the visible light is perpendicular to the polarizing direction of the polarizer. When the light on the target is brightest, the polarizing direction of the visible light is parallel to the polarizing direction of the polarizer. Thus, one can tell the polarizing direction of the visible light by observing the light on the target. Similar, one can qualitatively tell the intensity of the visible light by observing the brightness or darkness of the visible light.
A conventional apparatus for detecting the intensity of electromagnetic waves includes a photoelectric sensor and two electrodes connected, to the photoelectric sensor. In general, to detect the intensity of electromagnetic waves, the photoelectric sensor is irradiated by the electromagnetic waves. Thus, the incident electromagnetic waves can be transformed to electric signals by the photoelectric sensor, and the electric signals can be detected.
Carbon nanotubes (CNT) are a novel carbonaceous material having an extremely small size and an extremely large specific surface area. Carbon nanotubes have received a great deal of interest since the early 1990s, because they have interesting and potentially useful electrical and mechanical properties, and have been widely used in many fields. A disordered carbon nanotube film based apparatus for detecting electromagnetic waves is disclosed in “Bolometric infrared photoresponse of suspended single-walled carbon nanotube films”, Science, Mikhail E. Itkis et al, vol 312, P412 (2006). The carbon nanotubes have a uniform absorbability of electromagnetic waves having different wavelengths. When the disordered carbon nanotube film is irradiated by electromagnetic waves having different wavelengths, the resistance of the disordered carbon nanotube film changes. Thus, the intensity of the incident electromagnetic waves can be detected by detecting the resistance of the irradiated disordered carbon nanotube film.
However, the above apparatus can only detect the intensity of electromagnetic waves, and not the polarizing direction thereof.
What is needed, therefore, is to provide a method for detecting the polarizing direction of electromagnetic waves.